Download atomic physics worksheet

MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 15: REFLECTION AND REFRACTION
CLASS NOTES
ELECTROMAGNETIC SPECTRUM
Light is a form of energy. When we hear the word “light” we normally think of visible light that
radiates from the sun or a light bulb. In the scientific sense, light refers to the entire range of the
electromagnetic spectrum.
THE ELECTROMAGNETIC SPECTRUM
VISIBLE LIGHT
Visible light is the narrow frequency band of electromagnetic waves to which our eyes are sensitive.
Visible light wavelengths are measured in nanometers (1 nm = 10-9 meters). Visible light wavelengths
range from 400 nm (violet) to 750 nm (red).
SPEED OF LIGHT
Nothing in the universe travels faster than light. The speed of light c in a vacuum:
c = 3.00 x 108 m/s
(186,000 miles per second)
DRAWING LIGHT RAYS
Light waves from the sun and other objects travel great distances. By the time these light waves reach
the earth, they are parallel rays of light. A line drawn perpendicular to a surface where an incident ray
strikes the surface is called the normal line. Angles of reflection and refraction are measured relative
to the normal.
1|Page
PHYSICS
MR. SURRETTE
VAN NUYS HIGH SCHOOL
INCIDENT AND REFLECTED RAYS
REFLECTION/REFRACTION RULES
1. When an incident ray undergoes partial reflection and partial refraction, the incident, reflected and
refracted rays are all in the same plane.
2. The path of a light ray through a refracting surface is reversible.
3. As light travels from one medium into another, the frequency does not change.
THE LAW OF REFLECTION
The law of reflection states that the angle of incidence equals the angle of reflection:
 = ’
INDEX OF REFRACTION
Each transparent medium is characterized by the index of refraction n which equals the ratio of the
speed of light in the medium to the speed of light c in a vacuum :
n=c/v
(c = 3.00 x 108 m/s)
Example 1. If the velocity of light through an unknown liquid is measured at 2.40 x 108 m/s, what is the
index of refraction of this liquid?
1A.
(1) n = c / v
(2) n = 3.00 x 108 m/s / 2.40 x 108 m/s
(3) n = 1.25
Example 2. A beam of light in air is incident on the surface of a rectangular block of clear plastic (n =
1.49). If the velocity of the beam before it enters the plastic is 3.00 x 108 m/s, what is its velocity after
emerging from the block?
2A. 3.00 x 108 m/s
DIRECTION OF REFRACTION
Light rays bend towards the normal line as they pass into a denser medium. Light rays bend away
from the normal line as they pass into a lighter medium.
2|Page
PHYSICS
MR. SURRETTE
VAN NUYS HIGH SCHOOL
DIRECTION OF REFRACTION
SNELL’S LAW
Snell’s law is a law of refraction. This is one practical form of Snell’s law:
n = sin1 / sin2
Example 3. A ray of light in air is incident on an air-to-glass boundary at an angle of 30.0o with the
normal. If the index of refraction of the glass is 1.65, what is the angle of the refracted ray within the
glass with respect to
the normal?
3A.
(1) n = sin1 / sin
(2) sin2 = sin1 / n
(3) sin2 = sin30o / 1.65
(4) sin2 = 0.5 / 1.65
(5) sin2 = 0.303
(6) 2 = arcsin2 = 17.6o
Example 4: An underwater scuba diver sees the sun at an apparent angle of 45.0o from the vertical.
How far is the sun above the horizon? (nWATER = 1.33)
4A.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
n = sin 1 / sin 
sin 1 = (n)(sin 2)
sin 1 = (1.33)(sin 45o)
sin 1 = (1.33)(0.707)
sin 1 = 0.943
1 = arcsin 1 = 70.5o
The sun is 19.5o above the horizon.
3|Page
PHYSICS
MR. SURRETTE
VAN NUYS HIGH SCHOOL
DISPERSION AND PRISMS
As light travels from one medium into another, the frequency remains constant but the wavelength
changes:
n = o / n
Note: One result of dispersion is the rainbow of colors that emerges when white light strikes a prism.
TOTAL INTERNAL REFLECTION
Total internal reflection occurs when light rays traveling in a denser medium (n1) are incident on a
medium of lesser index of refraction (n2). Total internal reflection occurs at angles of incidence  > c
(sometimes this is written as i > Ic, read as “the incident ray is greater than the incident critical angle”.)
TOTAL INTERNAL REFLECTION
sin c = n2 / n1
sin Ic = n2 / n1
Example 5. If the critical angle for internal reflection inside a certain transparent material is found to be
48.0o, what is the index of refraction of the material? (Air is outside the material).
5A.
(1) sin c = n2 / n1
(2) n1 = n2 / sin c
(3) n1 = 1.00 / sin 48o
(4) n1 = 1.35
Example 6. A laser beam, incident at 30 degrees onto the surface of a block of glass, is partially
reflected and partially transmitted (with refraction) at the block’s upper surface. The index of refraction
of the glass is 1.5.
Example 6. Diagram
4|Page
PHYSICS
MR. SURRETTE
VAN NUYS HIGH SCHOOL
6a. The speed of light in a vacuum is
c = 3.00 x 108 m/s. What is the speed of light
in the glass expressed as a fraction of c?
A.
(1) n = c / v
(2) v = c / n
(3) v = c / (1.5)
(4) v = 0.67 c
6b. Is the angle of refraction greater than, less than, or equal to 30 degrees?
A. less than
6c.
A.
(1)
(2)
(3)
(4)
(5)
(6)
Calculate the angle of refraction in degrees.
n = sin 1 / sin 
sin 2 = sin 1 / n
sin 2 = sin 30o / 1.5
sin 2 = 0.5 / 1.5
sin 2 = 0.333
2 = arcsin 2 = 19.5o
6d. What is the angle the reflected beam makes with the normal?
A. 30 degrees. The angle of reflection = the angle of incidence, i.e. 1 = 1’.
SNELL’S LAW (re-visited)
Sometimes a light ray originates in a denser medium and escapes to a lighter medium. For these cases,
Snell’s law can be written:
n1sin1 = n2sin2
Example 7. A beam of light in water strikes a boundary with air. The index of refraction of water is
1.33.
7a.
A.
(1)
(2)
(3)
(4)
(5)
If the angle of incidence is 30 degrees what is the angle of refraction?
n1 sin1 = n2 sin2
sin2 = n1 sin1 / n2
sin2 = (1.33)(sin 30o) / 1
sin2 = 0.665
2 = arcsin 2 = 41.7o
5|Page
PHYSICS
MR. SURRETTE
7b.
A.
(1)
(2)
(3)
(4)
(5)
VAN NUYS HIGH SCHOOL
Calculate the critical angle for these rays.
n1 sin1 = n2 sin2
sin 1 = (n2)(sin 2) / (n1)
sin 1 = (1.00)(sin 90o) / (1.33)
sin 1 = 0.752
1 = arcsin 1 = 48.8o
7c. If the angle of incidence is 53 degrees what happens to the light at the boundary?
A. It is totally reflected.
6|Page
PHYSICS